Quick answer: A typical 1.5-ton split AC (about 1500W actual draw) costs roughly £0.37 per hour to run in the UK (at 24.5p/kWh) or $0.26 per hour in the US (at 17c/kWh). Running it 8 hours a night costs about £88/month in the UK or $61/month in the US. Use the calculator below with your own AC’s wattage and daily hours for an exact figure.
AC Running Cost Calculator
1 ton ≈ 1200W, 1.5 ton ≈ 1500-1800W, 2 ton ≈ 2000-2400W (actual running draw, not cooling capacity)
Compressor cycles on/off once the room cools – 50-70% is typical, use 100% for a “worst case” estimate.
Auto-filled with a typical average – edit to match your own tariff
How Much Does It Cost to Run an Air Conditioner?
The running cost of an AC depends on its power draw, how long it runs, and how often the compressor actually kicks in (its duty cycle). The formula is:
Cost = (Wattage / 1000) × Duty Cycle × Hours Used × Electricity Rate per kWh
An AC’s nameplate wattage is its power draw while the compressor is actively cooling – but the compressor doesn’t run non-stop. Once the room reaches the set temperature, the thermostat cycles the compressor off and only the fan keeps running at a fraction of the power. That’s why “duty cycle” (the percentage of time the compressor is actually on) matters so much for an accurate estimate – a well-sized AC in a well-insulated room might only run its compressor 40-50% of the time, while an undersized AC in a hot room can run close to 90-100%.
AC Running Cost by Size (Ton Rating)
| AC Size | Typical Power Draw | Cost/Hour (UK, 24.5p, 65% duty) | Cost/Hour (US, 17c, 65% duty) |
|---|---|---|---|
| 1 Ton | ~1200W | £0.19 | $0.13 |
| 1.5 Ton | ~1500-1800W | £0.26 | $0.18 |
| 2 Ton | ~2000-2400W | £0.34 | $0.24 |
| Window Unit (small) | ~900-1100W | £0.16 | $0.11 |
Worked Example: Running a 1.5 Ton AC Overnight
Say your AC draws 1800W, you run it 8 hours a night, the compressor cycles at a 60% duty cycle, and you pay 24.5p/kWh (UK average):
- Effective wattage = 1800 × 0.60 = 1080W
- Cost per hour = (1080/1000) × 0.245 = £0.26
- Cost per night (8 hrs) = £0.26 × 8 ≈ £2.12
- Cost per month (30 nights) = £2.12 × 30 ≈ £63.50
Raise the thermostat by just 2-3°C and the duty cycle typically drops 15-20 percentage points, which can shave £10-15 off that monthly figure without making the room noticeably less comfortable.
AC Running Cost by Star Rating (BEE Rating, India Context)
In markets like India that use BEE (Bureau of Energy Efficiency) star ratings, a higher star rating means the compressor uses less electricity to deliver the same cooling, which directly lowers running cost even at the same tonnage and usage pattern. Here’s roughly how monthly running cost compares for a 1.5-ton split AC run 8 hours/day at typical Indian electricity rates (~Rs 8/kWh):
| Star Rating | Approx. Power Consumption | Est. Monthly Cost (8 hrs/day) |
|---|---|---|
| 3 Star | ~1650W effective | ₹3,168 |
| 4 Star | ~1450W effective | ₹2,784 |
| 5 Star | ~1250W effective | ₹2,400 |
| 5 Star Inverter | ~950W effective (variable load) | ₹1,824 |
The gap between a 3-star and a 5-star inverter unit can be over ₹1,300 per month during peak summer usage, meaning the higher upfront cost of a better-rated AC is often recovered within one or two cooling seasons through lower electricity bills alone.
Formula Walkthrough: Step by Step
To turn your AC’s specs into a running cost estimate, follow these steps in order – this is exactly what the calculator above automates:
- Find the rated power input (watts): check the outdoor unit’s nameplate or the product spec sheet for “Rated Power Input” or “Running Watts,” not the BTU or ton rating.
- Estimate the duty cycle: this is the percentage of time the compressor is actually drawing full power rather than idling with just the fan running. A well-insulated room in mild weather might see 40-50%; a hot room with a slightly undersized AC might see 80-100%.
- Calculate effective wattage: multiply rated wattage by the duty cycle percentage. For example, 1500W at 65% duty cycle = 975W effective.
- Convert to kilowatts: divide effective wattage by 1000 (975W becomes 0.975 kW).
- Multiply by your electricity rate: effective kW × rate per kWh gives you cost per hour.
- Multiply by hours used: cost per hour × daily hours of use gives daily cost, and daily cost × 30 gives a monthly estimate.
5 Ways to Cut Your AC Bill
- Set the thermostat a few degrees higher – each degree above 22-24°C reduces compressor duty cycle and can cut running cost by 5-8%.
- Use a timer or sleep mode – most inverter ACs raise the set temperature gradually overnight, cutting the compressor’s workload once you’re asleep.
- Clean or replace the air filter – a clogged filter forces the compressor to run longer to reach the same temperature.
- Seal doors, windows and use curtains – stopping warm air from entering reduces how often the compressor needs to cycle on.
- Choose an inverter AC over a fixed-speed unit – inverter compressors modulate power instead of switching fully on/off, typically cutting running cost by 20-30%.
FAQs
How many watts does an AC use?
Actual running draw (not cooling capacity) is typically 900-1200W for a 1-ton unit, 1500-1800W for 1.5-ton, and 2000-2400W for 2-ton – but the compressor only runs part of the time, so real average draw is lower.
Does an AC run continuously or cycle on and off?
It cycles. Once the room reaches your set temperature, the compressor switches off and only the fan keeps circulating air at a much lower wattage, then the compressor kicks back in as the room warms slightly. This on/off pattern is the “duty cycle” used in the calculator above.
Is an inverter AC really cheaper to run?
Yes. A fixed-speed AC’s compressor is either fully on or fully off, while an inverter AC’s compressor adjusts its speed to match the exact cooling needed, avoiding wasteful full-power cycling. This typically saves 20-30% on running cost versus a similarly sized non-inverter unit.
What temperature should I set my AC to save money?
24-26°C (75-79°F) is generally the sweet spot between comfort and cost – every degree colder than that increases compressor duty cycle and running cost by roughly 5-8%.
How do I find my AC’s wattage?
Check the rating plate on the outdoor condenser unit – it lists “Rated Power Input” or “Running Watts” in W. Don’t use the BTU or ton rating directly, since that measures cooling capacity, not electrical draw.
Does room size affect AC running cost?
Yes – a larger or poorly insulated room takes longer to cool and needs a higher duty cycle (or a bigger AC) to maintain temperature, both of which increase running cost for the same number of hours used.
How Room Size Affects the Right AC Tonnage (and Running Cost)
Choosing an AC that’s undersized for the room forces the compressor to run at a near-100% duty cycle just to keep up, which drives running cost up even though the unit itself draws less power than a bigger one. Choosing the correct size for your room keeps the duty cycle in the efficient 40-65% range. A rough sizing guide for typical room heights and insulation:
| Room Size | Recommended AC Size |
|---|---|
| Up to 120 sq ft | 1 Ton |
| 120-180 sq ft | 1.5 Ton |
| 180-250 sq ft | 2 Ton |
| 250+ sq ft or direct sun exposure | 2.5 Ton or larger / multiple units |
If your room gets strong direct sunlight, has a high ceiling, or is on a top floor under a hot roof, size up one notch from this table – an undersized unit working overtime often ends up costing more to run than a correctly sized or even slightly larger one.
More Frequently Asked Questions
Is it cheaper to leave the AC on all day at a low setting or turn it on/off?
For short absences (under 1-2 hours), leaving it on a slightly higher setting is often similar in cost to turning it off, since cooling a hot room back down from scratch takes a burst of high compressor duty cycle. For longer absences, turning it off (or using a smart schedule) is almost always cheaper.
Does AC running cost differ between window units and split units?
Split ACs are generally more efficient than window units of the same tonnage because the compressor and condenser sit outside, reducing heat re-entering the room and allowing better airflow design. Window units tend to have a slightly higher effective running cost for the same cooling output.
How much does a 2-ton AC cost to run per month?
At a 65% duty cycle, 8 hours/day, and a mid-range electricity rate, a 2-ton AC typically costs more than double a 1-ton unit per month due to its higher wattage – use the calculator above with your own tonnage, hours, and local rate for an exact figure.